Area Forecast Discussion
Issued by NWS Upton, NY

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893 FXUS61 KOKX 240551 AFDOKX Area Forecast Discussion National Weather Service New York NY 151 AM EDT Fri Mar 24 2017 .SYNOPSIS... A warm front approaches tonight and moves across the region on Friday. An unsettled weather pattern then sets up this weekend and continues into the middle of next week. A back door cold front moves through Saturday afternoon and night. Low pressure gradually approaches from the west Sunday, and moves across on Monday. Another frontal system may impact the region Tuesday into Wednesday. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... With the surface ridge axis moving across the area late this evening, winds at the coast have either become SW or light and variable. This has resulted in significant differences in temperatures, due to radiational cooling, and dew points in a matter of hours have risen from zero into the lower 20s at some locations. As the southerly flow gradually increase late tonight, the airmass will become more homogeneous with temperatures leveling off or even rising. Clear to start, then clouds begin to increase late at night ahead of an approaching warm front. Models agree that it remains dry through the night. Clouds arrive too late to make much of an impact on low temperatures, which will be below normal. && .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM SATURDAY/... Isentropic lift and low-mid level shortwave energy pass through along with the surface warm front during Friday morning. The best combination of moisture and lift will be north and west of the city. It will then be dry by mid afternoon across the CWA. Have scaled back on PoPs somewhat from the previous forecast, but did not have enough confidence to drop it below likely over the far NW zones. Regarding PCPN types, expecting a short period of mixed PCPN before changing to plain rain as temps aloft warm up quickly. For the NW zones this mix starts out as mostly snow, and near the coast there could be a brief rain/sleet mix at the onset before changing to all rain. There is the potential of up to an inch of snow/sleet accumulation NW of the city before the changeover. There is also the chance that there`s freezing rain in the mix for a couple of hours for Orange and Putnam Counties and areas right near their borders. Thinking is that the changeover to plain rain will be too quick for a widespread freezing rain event, especially without an ideal cold air damming setup. Will therefore not issue any advisories at this time. High temperatures will be a little below normal. Dry during the nighttime with the warm front still to the north. This plus mostly cloudy conditions will lead to above normal low temperatures Friday night. && .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/... Unsettled weather pattern sets up across the region through the long term period. On Saturday, a split flow jet stream with polar jet running across the New England southern Canada border and southern stream cut-off across the south central United States. Weak ridging attempts to set up between these two streams. Surface high pressure across the western Atlantic pumps unseasonably warm air into the area under southwesterly flow. At the same time, a back door front will gradually sink south from New England. Deterministic models and ensembles all indicate strong high pressure pushing south out of southeast Canada, forcing the boundary south through the day on Saturday. The main question is with the timing. The ECMWF, NAM, and NAM-3km all bring the boundary south of Long Island by early afternoon. The GFS and CMC are a bit slower, bringing the boundary south by early evening. There is notable spread in the 15z SREF as well. The timing of the back door front will have be important with regards to temperatures. The slower timing will allow temperatures to warm well into the 50s, and possibly lower 60s. Faster timing will hold highs down, more in the 40s and 50s. Spread in the 15z SREF at BDR for high temperatures ranges from 44 to 60 degrees. Have generally sided with a consensus for this forecast, with the boundary moving south in the afternoon, allowing temperatures to warm into the middle and upper 50s. Upper level cutoff low opens Sunday night into Monday as the remaining shortwave passes near or just to our north. PoPs increase to likely this period with rain. Parent low will likely pass to the north, with possible secondary development along nearly stationary front near or just south of Long Island. High temperatures will ultimately be determined by where this boundary sets up. Current forecast shows readings in the 50s near the coast, and upper 40s inland. Shortwave passes east Monday night followed by weak ridging aloft. Progressive flow pattern leads to the continuation of unsettled conditions with models and ensembles signaling another frontal system approaching Tuesday, passing Tuesday night into Wednesday. Continued chances for rain and near seasonable temperatures are forecast. High pressure should follow for next Thursday. && .AVIATION /06Z FRIDAY THROUGH TUESDAY/... High pressure slides offshore tonight. A warm front then lifts to the north from Friday morning into Friday afternoon. Mainly VFR through the TAF period. There is the potential for some light precipitation on Friday morning into early afternoon. At this time confidence high enough for prevailing at KSWF which should see a wintry mix along with some MVFR cigs. Any accumulation should be less than 1 inch. Elsewhere else, will carry a TEMPO for light rain, except at KHPN where a wintry mix will be possible. light and variable winds increase out of the S-SSW this morning to around or just over 10 kt. Gusts around 20 kt likely this afternoon. Winds diminish overnight. .OUTLOOK FOR 06Z SATURDAY THROUGH MONDAY... .Friday night-Saturday morning...VFR. .Saturday afternoon-Monday...MVFR/IFR probable, possibly LIFR. .Monday night-Tuesday...MVFR or lower possible. && .MARINE... Tranquil conditions on all waters tonight into Friday morning with a high pressure ridge passing through. Winds and seas then increase Friday afternoon with the pressure gradient tightening. Expecting all but NY Harbor to see SCA conds in the afternoon, with advisory conds continuing into the night for the ocean, Eastern Sound and Eastern Bays. Lingering seas around 5 ft are possible east of Moriches inlet Saturday morning. Otherwise, winds and seas are expected to be below SCA levels on Saturday. Increasing easterly flow Saturday night into Sunday brings wind gusts near 25 kt on the ocean, with ocean seas approaching 5 ft. SCA winds are possible on LI Sound, LI Bays, and NY Harbor. The pressure gradient weakens Sunday night into Monday. Sub-SCA conditions are forecast on all waters through Monday night. The approach of a frontal system may build seas around 5 ft Tuesday afternoon. && .HYDROLOGY... Unsettled weather this weekend into early next week may result in an inch or more of precipitation. However, this would occur over a prolonged period, so no hydrologic concerns are anticipated. Snow melt across interior sections continues at a slow rate with a more significant snow melt on Saturday as temperatures rise to above normal readings. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...None. NY...None. NJ...None. MARINE...Small Craft Advisory from 10 AM this morning to midnight EDT tonight for ANZ330-340. Small Craft Advisory from noon today to 6 PM EDT this evening for ANZ335-345. Small Craft Advisory from 10 AM this morning to 6 AM EDT Saturday for ANZ350-353-355. && $$ SYNOPSIS...JC NEAR TERM...JC/DW SHORT TERM...JC LONG TERM...DS AVIATION...BC MARINE...JC/DS/DW HYDROLOGY...JC/DS

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